Question: Nihal ran $7$ kilometers in $21$ minutes. What was his average speed, in kilometers per hour?
Explanation: $21$ minutes is $\frac{21}{60} = \frac{7}{20}$ hours. His average speed in kilometers per hour is the number of kilometers he ran divided by the number of hours he ran, or $7 \div \frac{7}{20} = 7\cdot \frac{20}{7} = 20$ km/h.